Generally, pultrusion can be defined as a process for producing reinforced plastic geometrical shapes in a continuous length by pulling a resin impregnated fiber reinforcement through a forming and curing die. Pultrusion dates back to the early 1950's where it was initially used to form round bar stock for the fishing rod industry. The systems, method and apparatus for forming pultruded shapes remained at this level for several years until the late 1960's when improvements allowed manufacturers to form various structural shapes used in a number of applications including corrosive and weather resistant ladders, gratings, hand rails, hoods, walkway supports, and structural elements for buildings such as greenhouses and the like. Today, the pultrusion process is widely used in several countries for producing either hollow or solid reinforced composites in continuous lengths of constant cross section from 1/32 inch diameter rods to structural beams having flange dimensions of 8 inches or more.
In most applications, the pultruded shapes are assembled in a piece-by-piece manner using mechanical or chemical joining techniques. It has been found, however, particularly in those applications utilizing larger pultruded shapes to form trusses and other structural elements, that the joints of such structures are much more likely to fail than the pultruded sections therebetween using existing joining techniques. Moreover, the pultrusion technology developed to date is capable of producing only continuous lengths of fiber reinforced material having a constant cross section. Thus, formation of generally sharp curved corners in structural applications is not possible using present techniques.